Controlled release S-methoprene pesticide can offer advantages for pest control since the control materials can be released when needed and in controlled or effective amounts.
The invention relates to the control of aquatic pests that can emerge into adult flying insect pests in an aquatic location where pests hatch, mature and subsequently enter the terrestrial environment. The aquatic locations of the invention are often wet year around or are locations that are often dry, but can become episodically flooded creating a pestiferous aquatic location. If the periodic flooding of such dry areas result in a pest generating volume of water (about 1 cm or greater standing water) for a sufficient period of time (4 days at a minimum), the flooded area can create periodic populations of flying insect pests during the spring, summer and fall of the year. The treatment of aquatic breeding sites or loci involves the careful application of a control agent to the aqueous environment. A variety of aqueous control agents have been created. Sjogren, U.S. Pat. Nos. 4,732,762 and 4,971,796 disclose a briquette, granular or particulate form of a slow release pest control agent. The briquette form of the pest control agent comprises a cast, high compressive strength, plaster briquette that can slow the release of the pest control agent into the aqueous environment based on the dissolution rate of the high compressive strength plaster. The briquette can contain the pest control agent in a combination with a number of other ingredients that can stabilize the agent and to obtain a sustained level of controlled release. The granular form comprises a core, a coating and an effective amount of the pest control agent. Such a granular form can be distributed into the general environment including aquatic and dry aquatic sites. Levy, U.S. Pat. Nos. 5,858,386 and 6,512,012 teach enhancing the action of conventional pest control agent with a designed formulation using a surface filming material.
The Metropolitan Mosquito Control District of Minnesota has used the briquette form of the mosquito control agent by Sjogren. That technology has been licensed to Wellmark International to sell to other governmental agencies in the United States and elsewhere. In large part, these patents relate to the continuous, generally broadcast application over an aquatic surface of a pellet, powder, foam, spray, briquette or other material at a rate of about 2.5 to 20 pounds of treatment material per acre. The briquette is selectively placed in an aquatic site for mosquito control purposes. The patent suggests that the application of the briquette in a carefully placed location in an amount of about 1 briquette per each 200 square feet (6 square meters) of aquatic location at a treatment rate of about 200-400 grams of S-methoprene per acre or 4000 meters2 (about 0.02 to about 0.05 gram/meter−2) of an aqueous site.
Controlled release technology developments have recently occurred in many areas. Both macro and micro-encapsulation processes have been used. Capsules of ceramics, biodegradable polymers, porous supports, cellulosic derivatives, urethane compounds, plaster, gypsum and other supports have been made to separate the pesticide from the environment and to ensure a controlled release.
An effective pest control concentration is defined as that amount effective to kill greater than 50% of at least one form or stage of a pest in its life cycle, or a concentration effective to prevent development or maturation of a form or stage of the pest during its life cycle. The pesticide should be released by the pest control means at a rate such that an effective amount is released but little is wasted. Further, the pesticide composition and means should comprise natural materials, be non-toxic and biodegradable, and of low cost. Accordingly, a substantial need exists for a controlled release formula that is inexpensive, can deliver controlling concentrations for a useful period of time, typically for least 4 days, at least 30 days or for 40 to 120 days.